Stellar activity

Stellar activity is variation in a star’s brightness, spectrum, or surface driven by processes such as convection and magnetic fields. It includes phenomena such as starspots, flares, and stellar winds.

Stellar dynamo: A process in which motion within a star’s electrically conducting plasma generates and sustains magnetic fields. Convection and rotation can power the magnetic fields behind many forms of stellar activity.
Radial velocity method: A planet-detection technique that infers orbital motion from periodic shifts in a star’s spectral lines. Activity-driven line shifts can imitate or obscure a planet’s gravitational signal.
Solar cycle: The roughly 11-year cycle in the number of sunspots and other indicators of solar magnetic activity. It is the best-observed example of activity varying on a regular stellar timescale.
Stellar pulsation: Periodic expansion and contraction of a star caused by oscillations within its interior. Pulsation changes stellar brightness through rhythmic size and temperature changes, unlike magnetic surface activity.
Convection zone: A region in a star where energy is transported mainly by the rising and sinking of plasma. Its turbulent motions help drive magnetic activity in stars with outer convection zones.
Transit photometry: A method for finding planets by measuring the recurring dimming of a star as a planet crosses its disk. Starspots and flares can distort transit light curves and bias planet measurements.
Solar flare: A sudden release of magnetic energy in the Sun’s atmosphere, producing intense radiation and energetic particles. Solar flares provide nearby examples of the outbursts also seen on other stars.
Eclipsing binary: A binary star system whose orbit carries one star in front of the other as seen from Earth. Eclipses cause brightness variations through changing visibility rather than changing surface activity.
Starspot: A relatively cool, dark region on a star’s visible surface, usually associated with concentrated magnetic fields. Starspots create surface patterns and brightness changes as a star rotates.
Stellar age dating: The estimation of a star’s age from properties that change over its lifetime. Magnetic activity and rotation provide age clues, especially for relatively young stars.

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